This is a basic question: how do you use index cards when writing a book or research paper? I've heard of people using them but I've never ever used them myself.

one way to use index cards is to write down all info on the current research book you are using, so when it comes time for bibliography to be written, you only have to alphebitize cards, not a list, and it's much easier. Another way is to write down evidence on cards (quote, page number, book) so when you use them in your paper you can give correct MLA format, and you don't have to look in the book all the time. These are just a few uses...

If you want an easy way to cross reference them....
Use a hole punch to make holes around the edge... depending on how many subjects the reference is appropriate for..
Then when you want to sort by some criteria.... you just stick an icepick into the holes.. and the proper ones come right out....